1. Field of the Invention
This invention relates to a polar axis finder for an equatorial mounting telescope.
2. Description of the Prior Art
In observing celestial bodies with an equatorial mounting telescope, its polar axis must be exactly in parallel with the axis of rotation of the earth. For this purpose, a polar axis finder for setting the polar axis with the Polaris in the sky as a target is commercially available.
However, as is well known, the Polaris is not on the true north pole, i.e. it is deviated by an angle of about fifty minutes (50') therefrom. Therefore, the conventional polar axis finder employs the following method: A circle is marked on the focus mirror in the polar axis finder by taking the deviation of fifty minutes into account. The eyepiece cylinder of the polar axis finder is made rotatable, and a local sidereal time scale is marked on the outer wall of the eyepiece cylinder. The local sidereal time at an observing position is calculated from the Greenwich apparent sidereal time by using a physical chronological table and the direction of deviation of the Polaris from the true north pole is calculated to set a scale. The polar axis of the main telescope is moved to a selected one of divided graduations in the circle marked on the focus mirror which is moved in association with the eyepiece cylinder, or the polar axis is moved into a small circle in the circle, to catch the Polaris, to thereby exactly set the polar axis.
However, this method is disadvantageous in that it takes a relatively long time to perform such intricate calculations. Furthermore, since celestial bodies are usually observed in the nighttime, it is considerably troublesome to perform such calculations.